In operation, a wireless communication devices use a portion of a particular radio frequency spectrum for wirelessly transmitting and receiving information. Regulatory bodies control the particular frequency spectra for mobile communication systems, and detailed definition typically made by standardization organizations. However, in general, each spectrum is divided into different frequency bands, with each band defined as a portion/range of the various frequencies allocated for certain type of usage, either licensed to a specific network operator or unlicensed for usage by anyone.
In modern wireless systems, frequency bands can be defined in order to operate in one out of two principal modes: time division duplex (TDD) or frequency division duplex (FDD). In a time division based system, each mobile terminal (e.g., user device) and/or base station in the communication system uses one single radio frequency range for both signal transmissions and receptions. To avoid direct interference between transmitted and received signals, each terminal is switched in time between transmission and reception functions. In a frequency division mode, two different frequency ranges are allocated for transmission and reception respectively. Accordingly, mobile terminals using FDD can transmit and receive signals simultaneously. In this manner the transmitted signal from the terminal antenna(s) will not interfere with the signals to be received in the same physical antenna(s) although the transmitter and receiver are operating at the same time.
Examples of frequency band definitions include frequency bands defined by the 3rd Generation Partnership Project (3GPP) for usage in wideband code division multiple access (WCDMA) and LTE systems. The bands are defined in 3GPP TS 25.101 and 36.101.
A recent development in wireless communication systems includes the usage of multiple frequency bands for simultaneous transmission between a base station and a terminal. Generally speaking, the concept is referred to as multi-carrier operation or carrier aggregation. The term “carrier” in this description refers to a carrier or center frequency of a particular frequency band. When utilizing carrier aggregation, the communication system can be configured to combine spectra from two or more bands into one larger aggregated spectrum resource. This can be done in many different configurations, e.g., by combining two or more bands for additional base station to terminal (e.g., downlink) bandwidth and/or by combine bands for terminal to base station (e.g., uplink) aggregation.
Unfortunately, a potential consequence of carrier aggregation may be intra-device interference, occurring between simultaneously transmitted and received signals.